Microsoft confirms a known issue in Windows 10 KB4535996

Windows 10 KB4535996 is another roller coaster ride for some
people with many users reporting boot failures, slow boot,
reduced performance, and SignTool.exe crashes. As always,
Microsoft hasn’t issued any warnings for Windows 10 owners and
official workaround to deal with the latest disaster is also
not available.

According to numerous user bug reports picked up by us, Windows
10 KB4535996 has several critical issues. As per the user
reports, Windows 10 KB4535996 may have the following serious
bugs:

Slow boot: After the power button is pressed, Windows 10
takes a long time to boot to the lock screen and login time has
also increased. Task Manager reveals that Windows 10 resources
are under normal usage.

System freezes and crashes: Apps such as Task Manager, File
Explorer or the desktop and taskbar crashes without warning.

Blue Screen of Death: Users are reporting that the
traditional BSOD error has returned back. On Windows 10, a Blue
Screen of Death will happen after a critical error. Generic
error messages such as “Your PC ran into a problem and needs to
restart” are displayed.

Reduced performance: In games, some users have noticed FPS
drops and audio stutters. I’ve also noticed reduced performance
for general activities.

Black screen during sign-in and other random times.

The update is also causing SignTool.exe to crash with generic
error messages. In a community post, Microsoft confirmed this
known issue and promised that a fix will be available in
mid-March.

“We’re aware of issues with signtool.exe after installing the
latest optional update for Windows 10, version 1903 or Windows
10, version 1909 (KB4535996). If you are encountering issues or
receiving errors related to signtool.exe, you can uninstall the
optional update KB4535996,” the company said.

Microsoft has to acknowledge the BSOD, slow boot time and
performance issues with the optional cumulative update.
Unfortunately, Microsoft’s support team is also clueless about
the recent update issues and the official workaround is still
not available.

If your PC is buggy after the update, you can uninstall the
patch by following these steps:

Head to Update & Security

Click ‘View update history’

Click ‘Uninstall updates’ link’

Select the KB number and uninstall the update.

After the patch has been removed, open the same page again and
pause the update for seven days.